1. Field of the Invention
This invention relates to a light beam recording system for recording an image on a recording material by scanning the recording material with a light beam, and more particularly to a device for correcting the pitch of the scanning lines by correcting the vibration of the vibrating mirror for vertical deflection of the light beam in the light beam recording system.
2. Description of the Prior Art
A light beam scanning type image recording system is used for instance in a laser COM (computer output microfilmer) which records the output data of a computer on a microfilm. The laser COM uses a laser beam for recording the image on a recording material such as a heat-mode recording film. Further, in the laser COM, there is used a two-dimensional light deflecting system which deflects a read-out light beam and a recording light beam having different wavelengths. The two-dimensional light deflecting system employs a rotating polygonal mirror for horizontal deflection and a vibrating mirror for vertical deflection such as a galvanometer mirror.
The galvanometer mirror has a defect in that the amplitude thereof changes as the temperature changes. When a galvanometer mirror is used for vertically deflecting the light beam, therefore, the pitch of the scanning lines or the intervals between the scanning lines are reduced as the temperature rises. The reduction of the pitch results in compression in the vertical direction of the recorded image. SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a device for automatically correcting the pitch of the scanning lines caused by the fluctuation in the amplitude of vibration of the vibrating mirror in a light beam scanning type image recording system.
A more specific object of the present invention is to provide a device for correcting the pitch of the scanning lines in a light beam recording system to prevent the image recorded thereby from being compressed when the temperature of the recording system rises.
The device in accordance with the present invention employs an optical mark on a linear encoder at a position where the mark receives several scanning lines near the end of scanning in the linear encoder, counts the number of the scanning lines crossing the optical mark to detect the fluctuation in the pitch of the scanning lines, and controls the gain of the drive circuit for a galvanometer mirror according to the fluctuation detected.
When the temperature of the light recording system rises and the amplitude of vibration of the galvanometer mirror is reduced, the pitch of the scanning lines is reduced and the number of scanning lines crossing the optical mark increases. Therefore, by counting the increased number of the scanning lines, the fluctuation in the pitch of the scanning lines can be known. Thus, by varying the gain of the mirror drive circuit according to the fluctuation in the pitch of the scanning lines, the pitch can be controlled at a constant value.